1. Field of the Invention
The present invention relates to a catalyst for reforming hydrocarbon with steam and, more particularly, to a catalyst for reforming hydrocarbon with steam, which has a high catalytic activity and a long catalyst life as well as which can appropriately be utilized, for example, for plants for manufacturing hydrogen for fuel cells or compact hydrogen manufacturing plants.
2. Description of Related Art
Various catalysts have been proposed as catalysts for promoting the reaction for reforming a hydrocarbon with steam into hydrogen, carbon monoxide, carbon dioxide and methane. For example, Japanese Patent Examined Publication (kokoku) No. 29,435/1964 discloses a catalyst for reforming the hydrocarbon with steam, which has a platinum group metal deposited on a heat-resistant oxide. This patent publication, however, does not refer to the structural feature of a simple substance for the catalyst composition.
Japanese Patent Unexamined Publication (kokai) No. 50,533/1982 discloses a porous alumina body with nickel oxide deposited thereon, which is characterized in that the volume of fine pores having pore sizes ranging from 60 to 120 Angstroms is 0.35 ml per gram or more and the volume of fine pores having pore sizes of 120 Angstroms or larger is 0.1 ml per gram or more.
Japanese Patent Unexamined Publication (kokai) No. 112,840/1984 discloses a catalyst composition for manufacturing fuel gases, which uses a catalyst carrier in which the pore volume of the micropores having pore sizes ranging from 100 to 10,000 Angstroms accounts for 40% or more of the total pore volume of the carrier.
The conventional catalysts including those described hereinabove, however, present the problem that they cannot satisfy increasing demands from the industry sector for catalysts with higher catalytic activity and longer catalyst life.
For instance, plants for manufacturing hydrogen for fuel cells, and so on, have made demands to develop catalysts for reforming with steam having the catalyst life longer than those used for existing devices for manufacturing hydrogen. However, nickel catalysts industrially available as of today as the catalyst for reforming with steam cause carbon to precipitate on a surface of the catalyst to an extremely large extent so that they do not provide the long catalyst life as desired.
Therefore, recently, much attention is focused on a catalyst system with a noble metal deposited on a zirconium type carrier, not on the nickel type catalysts, as a catalyst system having a high catalytic activity at low temperatures and suppressing deposition of carbon.
Japanese Patent Examined Publication (kokoku) No. 2,922/1977 discloses a catalyst for reforming with steam consisting of nickel and/or cobalt, a platinum group metal, an alkaline earth metal and a refractory support material such as zirconia. However, this publication does not provide any working example about cobalt and specify the kind of the alkaline earth metal. Further, little review has been made of the effect on the catalyst life.
Japanese Patent Unexamined Publication (kokai) No. 91,844/1981 indicates that a catalyst with rhodium deposited on the zirconia carrier has a catalytic activity higher than the nickel type catalyst. This publication, however, does not provide any review of its catalytic life, and there is the problem that the catalytic life of the rhodium/zirconia catalyst is insufficiently long.
Further, Japanese Patent Unexamined Publication (kokai) No. 38,239/1988 discloses that the catalyst for reforming with steam in which ruthenium and barium are deposited on the alumina carrier is higher in catalytic activity than other catalysts. This publication is also silent about the catalytic life and the alumina carrier is not said to be appropriate for ruthenium.
A. Igarashi et al. (A. Igarashi et al.: 62nd Shokubai Toronkai; 3B305, Sendai) indicate that catalysts having rhodium and a variety of oxides as a third component deposited on the zirconia carrier are higher in catalytic activity at low temperatures. This report, however, does not refer to the catalytic life, and the catalytic life cannot be anticipated from data of catalytic activity because there is not necessarily any relationship of the order of the catalytic activity at low reaction temperatures with the catalytic life.